1. Technical Field
This invention relates to the technology of sand core making, and more particularly to bonding sand core parts together to create a complex core assembly that enhances casting quality.
2. Discussion of the Prior Art
Sand core and mold assemblies for making complex metal castings are currently bonded together commercially by use of pastes applied to one of the mating surfaces of the cores to be joined. Pressure is needed to mate the mating core parts together and the use of such pressure often squeezes paste out from between the mating surfaces onto critical molding surfaces for defining the metal casting; the excessive paste will cause defective cast parts. The procedure is also disadvantageous because such mating pressure may impart undue stress to the fragile core parts, causing defects, and requires excessive setting and curing time, often about 30 minutes.
A recent attempt to bond cores together without interrupting critical molding surfaces is disclosed in U.S. Pat. No. 4,932,459 wherein a sand and curable binder mixture is blown into a keyway of a core assembly to mechanically lock the core parts together by groove and tongue coupling. This requires separate sand blowing steps, one for the core parts and one for the keyway, adding to the cost of the procedure. For this approach, the sand core parts must be designed to mate with special overhanging surfaces to make the joint work effectively, part design does not always allow the use of this process particularly with small, fragile cores because a thick core cross-section is needed. Moreover, the joint is not firm and strong because of the lack of adhesive.